As it is well known, a device with a micro-electro-mechanical system (MEMS) is a micro device, which integrates the mechanical and electrical functions in a silicon chip or die realized by using the lithographic techniques of micro-manufacturing. The final assembled device is, typically made of the MEMS silicon die and optionally of integrated circuits for specific applications (application specific integrated circuits or ASICs) mounted on a substrate, for example of the LGA or BGA type (Land Grid Array or Ball Grid Array), flanked or piled onto the MEMS device, using conventional assembling processes.
In fact, it is well known that integrated circuits (IC) are manufactured on the surface of a semiconductor wafer and subsequently singulated in different semiconductor devices, or “dies”. Since the material of a semiconductor wafer—commonly silicon—tends to be relatively fragile, the dies are usually mounted on protective housings, or packages prior to the connection to a printed circuit board (PCB), the package ensuring the interconnection between the dies and the board.
It is also known that the substrate of the LGA/BGA type is covered by tracks of layers of conductive materials (usually copper), insulated from each other by layers of insulating or dielectric material. Conductive holes, called “vias”, are typically realized through the insulating layers with a vertical orientation with respect to the conductive layers, to form conductive paths between conductive tracks present on different insulating layers.
A first embodiment of this type of device with micro-electro-mechanical system (MEMS) realized on a substrate LGA/BGA and subsequently encapsulated in a package is shown with reference to FIG. 1.
On a substrate 1, of the LGA/BGA type, having an upper surface 2 and a lower surface 3, a MEMS device 4 is glued comprising a silicon die having an active surface 5 and a non active surface 6 opposed to the active surface 5. In particular, in the silicon die, in correspondence with the active surface 5, a membrane 7 is integrated to realize a pressure sensor.
The non active surface 5 of the silicon die is glued onto the upper surface 2 of the substrate 1.
The active surface 5 is then electrically connected to the substrate 1 by means of a conductive wire 8, for example through the conventional wire-bonding technique.
A cap 9 provided with an opening 9a is then overlapped onto the MEMS device 4 and onto the electric connections 8 and fixed onto the upper surface 2 of the substrate 1 so as to protect the MEMS device 4.
The presence of the opening 9a allows the MEMS device 4 to communicate with the environment outside the cap 9, for sensing variations of fluids such as, for example, air or water.
A second embodiment of this type of micro-electro-mechanical system device (MEMS) realized on a substrate LGA/BGA and subsequently encapsulated in a package is shown with reference to FIG. 2.
Elements being structurally and functionally identical with respect to the package described with reference to FIG. 1 will be given the same reference numbers.
In this embodiment the MEMS device 4 communicates with the outer environment by means of an opening 1a realized in a portion of the substrate 1 physically connected to the MEMS device, while the cap 9 is completely closed.
Although advantageous under several aspects, this solution shows a drawback in that the cap 9 must be suitably manufactured and fixed onto the upper surface 2 of the substrate 1.
Improved packages, in particular for MEMS devices, are needed having structural and functional characteristics so as to allow avoiding the construction of caps and overcoming the drawbacks still limiting the packages realized according to the prior art.